U.S. Pat. No. 3,825,364 shows an outer wall which is completely porous. There is a cavity between this wall and a substrate.
U.S. Pat. No. 5,080,557 shows a layer structure comprising a substrate, a porous interlayer and a completely sealed outer layer.
U.S. Pat. No. 4,318,666, compared to U.S. Pat. No. 5,080,557, additionally shows cooling passages in the substrate, to which a porous interlayer and a sealed outer layer have been applied.
JP 10-231 704 shows a substrate with cooling passages and a porous interlayer.
PCT/EP02/07029 and U.S. Pat. No. 6,412,541 show a porous structure within a wall, with the wall again having a coating on the outer side. The wall and the coating have cooling passages.
An article “Pore Narrowing and Formation of Ultrathin Yttria-Stabilized Zirconia Layers in Ceramic Membranes by Chemical Vapor Deposition/Electrochemical Vapor Deposition” by G. Cao et al. is known from the Journal of American Ceramic Society 1993, describing the deposition of a ceramic within a porous ceramic.
However, the known layer structures in some cases have inadequate cooling properties.